The disclosure relates to multimode optical fibers and methods for their manufacture, and more particularly to methods for imparting perturbations to multimode optical fibers and the resultant optical fibers.
High bandwidth multimode fibers are attractive for data center applications. In order to obtain high bandwidth, multimode optical fiber refractive index profiles are typically designed to exhibit an alpha-profile shape having an with alpha between about 1.7 and 2.3. However, optical fiber bandwidth can be sensitive to refractive index profile fluctuations and errors that inevitably occur during the manufacturing process. These profile fluctuations and errors can be divided into two types: alpha error and non alpha error. An alpha-error is an overall profile deviation from an ideal alpha-profile. Non-alpha errors are relatively small index fluctuations around an ideal profile such as centerline defect, profile diffusion tail, and random index fluctuations such as small spikes or dips that occur in the refractive index profile. It is believed that the non-alpha errors can tend to split modes in each mode group, thereby increasing the time delay spread between all of the mode groups. Such non-alpha errors are very difficult to entirely avoid in practical optical fiber manufacturing processes. One way to fix the non-alpha errors is to improve profile controls in fiber manufacturing process. However, it is very hard to reduce all minor index fluctuations to the point where high bandwidth (e.g. 3-4 GHzKm or greater) can be achieved.